The environmental impacts of replacing mineral oil with rapeseed oil in chainsaw lubricants are described using comparative life-cycle assessment (LCA). This LCA was part of a study which, through combination of LCA and CBA (cost-benefit analysis), described the environmental and socio-economic impacts of replacing mineral oil with rapeseed oil in several products. Chainsaw oil was chosen as an example because there is considerable interest in replacing mineral oil-based products with biodegradable products in applications where spillage or loss could be environmentally damaging, and chainsaw oils are lost to the environment during use.

Methodologies are outlined, and results presented from lifecycle inventories of energy consumption and emissions, for chainsaw lubricants produced from mineral oil or rapeseed oil in the UK. Global warming potential (GWP) impacts were lower for rapeseed chainsaw oil, in all scenarios, than for the mineral oil product. However other parameters illustrate that both assumptions (i.e. whether to examine the total or marginal impacts) and allocation of impacts can strongly influence conclusions. The most realistic scenario (70% allocation, with winter wheat impacts subtracted from those of oilseed rape) indicated that environmental impacts are less with the rapeseed oil product.

Keywords: life-cycle assessment, rapeseed oil, chainsaw lubricants

Introduction

The aim was to perform a comparative cradle-to-grave life-cycle assessment (LCA) on chainsaw lubricants made from either mineral oil or from rapeseed oil, in the UK. This LCA was part of a study which, through combination of LCA and CBA (cost-benefit analysis), described the environmental and socio-economic impacts of replacing mineral oil with rapeseed oil in several products. The inventories compiled for this LCA formed the basis of impact valuation through CBA; the CBA valuation phase is not reported in this paper.

Chainsaw oil was chosen as an example because there is considerable interest in replacing mineral oil-based products with biodegradable products in applications where spillage or loss could be environmentally damaging: chainsaw oils are lost to the environment during use, and are frequently used in environmentally sensitive areas. Chainsaw bar lubricants reduce friction between the chain and cutting bar of both motor manual chainsaws and automated harvester machines. They comprise a base oil (either mineral or vegetable), plus a package of performance-enhancing additives. The LCA was based on ‘model’ chainsaw lubricants with typically used additives.

Goal Definition and Scoping

The Functional Unit for chainsaw oil was defined as the volume used in cutting 1000 m3 of wood, assuming 80% harvester and 20% manual chainsaw use, in UK softwood plantations. This was derived using the oil consumption figures given by Kytö (1993). Thus the Functional Unit (FU) for rapeseed chainsaw oil was 34 litres, and for mineral chainsaw oil was 56 litres. The lifecycle stages of the chainsaw bar lubricants are shown in Fig. 1.

Fig. 1 Lifecycle of chainsaw lubricants made from mineral or rapeseed oil

Methodology

Inventories of inputs and emissions were compiled for each stage of the lifecycle. In the production of rapeseed oil, it was considered realistic to compare the marginal costs of crop production and crushing, rather than the total costs. This takes into account emissions such as nitrous oxide which are released from the soil whether a crop is grown or not. Consequently two alternative crop production scenarios (winter wheat and set-aside) are considered, relative to that of winter oilseed rape which is used to produce the chainsaw bar oil. This is justified on the basis that the land required to produce a specific quantity of rapeseed oil-based lubricant will be land transferred out of winter wheat production or set-aside.

A yield of 3.3 t seed per ha is assumed for winter oilseed rape; 1 t seed producing 0.41 t of blended oil (Booth et al., 1993). Thus, 1.35 t rapeseed oil are produced per ha, and the FU of 34 l is produced on 231 m2 of land. This area is designated the Functional Unit of land, and comparisons with the alternative crop production scenarios are based on this area, since there are no comparable end- products. Comparison between the alternative crop production scenarios is therefore on a cradle-to-farmgate basis only.

Boundaries

Arable cropping was assumed to take place between August 1995 and August 1996 on a UK arable farm with clay-loam soil, no animals, and all straw chopped with the combine. It was assumed that soil fertility would be the same, regardless of inclusion of oilseed rape or set-aside in the rotation. For both chainsaw oils, it was assumed that all crushing, refining, blending, packaging and use operations were carried out in the UK. For mineral oil, it was assumed that 80% was from UK offshore sources and 20% was from the Middle East.

Crop production and crushing stages

The product lifecycle is assumed to start with ploughing of the land in preparation for crop production in the autumn, and end after the lubricant has completely degraded in the environment. Winter oilseed rape production is considered on main scheme, rotational arable land. Data for energy requirements and emissions from each of the crop production stages were derived from Audsley et al. (1997), and include: materials input, manufacturing, repairs and maintenance of the farm machinery; production and use of fuels in tractors and seed/grain drying; construction, maintenance and demolition of buildings for machinery storage; production of fertilisers and pesticides; transport. It is assumed that 6.89 kg of fuel oil are required to dry one tonne of seed/grain. Allowance was made for seed production in all energy requirements and emissions.

Nitrate leaching emissions were estimated using the SUNDIAL N-model developed by the Institute of Arable Crop Research (IACR) at Rothamsted, UK (Table 1); all scenarios were assumed to be in a rotation after two years of winter wheat. Nitrous oxide (N2O) emissions were estimated by specialists at SAC (Ball, pers. comm., 1997) (Table 1). Emissions from pesticide application have not been included. Transport of inputs to the farm are included in this stage.

Table 1. Estimated nitrate leaching and nitrous oxide emissions

NO3- (kg/ha)

N2O (kg/ha)

Winter oilseed rape

96

1.5

Winter wheat

148

0.25

Set-aside

48

1.0

The distribution of fuels used in electricity generation are based on UK figures (Anon, 1997), but emissions from electricity production are based on European figures (Audsley et al., 1997) as UK figures were not available. Energy data for crushing oilseed was taken from the EU ALTENER report (Anon, 1995); oil extraction is estimated to use 0.9 kg hexane/t seed (Anon., 1995; Cargill plc, pers.comm).

Mineral oil production

The product lifecycle is assumed to start with mineral oil exploration and production activities, and end after the lubricant has degraded in the environment. Data for most of the mineral oil production and refining stages have been derived from Boustead (1993b). For this study it was assumed that replacement of mineral oil by rapeseed oil will reduce overall crude mineral oil production by the volume substituted. Inputs and emissions associated with crude oil production and refining are split between the final oil products in the ratio of their production on a mass basis.

Distribution and packaging

Finished lubricants were assumed to be transported an average distance of 644 km by road haulage (truck) in 5 l containers made from HDPE (High Density Polyethylene). Inputs and outputs associated with road transport are from Audsley et al. (1997).

Use

Input and output data were derived from Mortensen et al. (1997). Rapeseed oil is completely biodegradable whereas mineral oil is more persistent. However, the mineral oil emitted is assumed to eventually degrade, with consequent emissions of CO2 which contribute to the global warming potential. In contrast, rapeseed oil is a renewable resource, and CO2 emissions from its degradation will be assimilated in subsequent crops, thus giving no net contribution to global warming.

Inventory, Classification and Characterisation

In the rapeseed oil LCA, the total impacts are given in the winter oilseed rape (OSR) scenario, and the marginal impacts are provided by subtracting the impacts associated with either winter wheat (WW) or set-aside (S/A). In the above total LCA of rapeseed oil-based chainsaw lubricant, all inputs and emissions associated with oilseed rape production and crushing were assigned to the oil. However, crushing of oilseed produces both oil and meal. As a sensitivity analysis, an allocation based on 70:30 oil:meal was defined on a mass x economic value basis, using an economic value averaged from oil and meal prices in August 1996 and 1998. The environmental impacts on Global Warming Potential (GWP) and Nutrient Enrichment, with and without allocation, are shown in Figs 2 and 3 respectively.

Fig. 2 GWP for LCA of chainsaw oil

Fig.3 Nutrient enrichment potential for LCA of chainsaw oil

Conclusions

The use of rapeseed chainsaw bar oil provides a significant advantage over mineral oil-based chainsaw oil, in terms of Global Warming Potential (GWP), regardless of assumptions or allocation. However, allocation and the alternative land-use assumptions had a large influence on the other impacts studied, as demonstrated by the nutrient enrichment potential results. The most realistic scenario was 70% allocation, with oilseed rape replacing winter wheat (i.e. 70%OSR-WW). For this scenario, all the environmental impacts considered are lower for chainsaw lubricant made from rapeseed oil than from the comparable mineral oil product.

Acknowledgements

This work was supported by MAFF (Ministry of Agriculture Fisheries and Food), UK.

SAC receives financial support from the Scottish Office Agriculture Environment and Fisheries Department.